[Win] Adjust build order to reduce flakiness.

* WebKit.vcxproj/WebKit.sln: Make sure WebCoreGenerated doesn't
  start until the last JSC tool has finished building.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@173063 268f45cc-cd09-0410-ab3c-d52691b4dbfc